MATERIALS AND METHODS: Sound extracted human molars were randomly divided into: manufacturer's instructions (MI), manual blend 2 mm (MB2), and manual blend 4 mm (MB4). Occlusal enamel was removed and flattened, dentin surfaces were bonded by Prime & Bond universal (Dentsply and Optibond FL, Kerr). For the MI group, adhesives were applied following the manufacturer's instructions then light-cured. For MB groups, SDR flow+ bulk-fill flowable composite resin was applied in 2- or 4-mm increment then manually rubbed by a micro brush for 15 s with uncured dentine bonding agents and the mixture was light-cured. Composite buildup was fabricated incrementally using Ceram.X One, Dentsply nanohybrid composite resin restorative material. After 24-h water storage, the teeth were sectioned to obtain beams of about 0.8 mm2 for 24-h and thermocycled micro-tensile bond strength at 0.5 mm/min crosshead speed. Degree of conversion was evaluated with micro-Raman spectroscopy. Contraction gaps at 24 h after polymerization were evaluated and atomic force microscopy (AFM) nano-indentation processes were undertaken for measuring the hardness across the interface. Depth of resin penetration was studied using a scanning electron microscope (SEM). Bond strength data was expressed using two-way ANOVA followed by Tukey's test. Nanoindentation hardness was separately analyzed using one-way ANOVA.
RESULTS: Factors "storage F = 6.3" and "application F = 30.11" significantly affected the bond strength to dentine. For Optibond FL, no significant difference in nanoleakage was found in MI/MB4 groups between baseline and aged specimens; significant difference in nanoleakage score was observed in MB2 groups. Confocal microscopy analysis showed MB2 Optibond FL and Prime & Bond universal specimens diffusing within the dentine. Contraction gap was significantly reduced in MB2 specimens in both adhesive systems. Degree of conversion (DC) of the MB2 specimens were numerically more compared to MS1 in both adhesive systems.
CONCLUSION: Present study suggests that the new co-blend technique might have a positive effect on bond strengths of etch-and-rinse adhesives to dentine.
METHODS: Dentine surfaces were etched with 37% phosphoric acid, bonded with respective in vitro ethanol and acetone adhesives modified with (m/m, 0, 1%, 2% and 3% ribose), restored with restorative composite-resin, and sectioned into resin-dentine slabs and beams to be stored for 24h or 12 months in artificial saliva. Bond-strength testing was performed with bond failure analysis. Pentosidine assay was performed on demineralized ribose modified dentine specimens with HPLC sensitive fluorescent detection. The structural variations of ribose-modified dentine were analysed using TEM and human dental pulpal cells were used for cell viability. Three-point bending test of ribose-modified dentine beams were performed and depth of penetration of adhesives evaluated with micro-Raman spectroscopy. The MMP-2 and cathepsin K activities in ribose-treated dentine powder were also quantified using ELISA. Bond strength data was expressed using two-way ANOVA followed by Tukey's test. Paired T tests were used to analyse the specimens for pentosidine crosslinks. The modulus of elasticity and dentinal MMP-2 and cathepsin K concentrations was separately analyzed using one-way ANOVA.
RESULTS: The incorporation of RB in the experimental two-step etch-and-rinse adhesive at 1% improved the adhesive bond strength without adversely affecting the degree of polymerisation. The newly developed adhesive increases the resistance of dentine collagen to degradation by inhibiting endogenous matrix metalloproteinases and cysteine cathepsins. The application of RB to acid-etched dentine helps maintain the mechanical properties.
SIGNIFICANCE: The incorporation of 1%RB can be considered as a potential candidate stabilizing resin dentine bond.